JP4112505B2 - Optical microphone and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high-performance and small-sized microphone used in speech recognition and the like, and more particularly, to an optical microphone using a micro electromechanical system (MEMS) technique and a manufacturing method thereof.

  There is a condenser microphone as a small microphone. The condenser microphone detects the amount of vibration displacement of the diaphragm from the change in capacitance with the lower electrode.

Also, the reflection type is the mainstream as the optical microphone. A vertical surface-emitting light-emitting element with a substantially uniform emission intensity distribution and a concentric light-receiving element around it are adopted, and the difference between the outputs from multiple light-receiving elements as differential signals An optical microphone that detects and outputs an output has also been proposed (see Patent Document 1). In the invention described in Patent Document 1, the influence of the temperature change or drive current change of the light emitting element is reduced and a stable signal output is obtained as compared with the case of using a single light receiving element as an output signal. .
JP 2001-169394 A

  Since the condenser microphone detects the vibration displacement amount of the diaphragm from the change in capacitance with the lower electrode, it cannot realize sharp directivity. For this reason, a “microphone array” that uses a plurality of condenser microphones and realizes unidirectionality by using the delay sum is required. In addition, the sensitivity of the condenser microphone is improved as the gap between the diaphragm and the lower electrode is smaller. However, the stability is lacking, and the gap between the diaphragm and the lower electrode often becomes a problem in the gap formation process, resulting in a decrease in yield. It is a factor.

  If the optical microphone is of a reflective type, the back surface of the diaphragm can be opened, so that an ideal 8-shaped bi-directionality that captures sound from all directions and cancels out ambient noise can be obtained. However, since the reflected light generally has a larger spread than the incident light, it is difficult to observe the minute vibration displacement of the diaphragm as a large difference in the reflected light intensity. Since a transmission line is added, various problems such as an increase in cost, an enormous system, and a limited use range have arisen.

  In view of the above problems, an object of the present invention is to provide an optical microphone that has high directivity, is small and thin, and is environmentally resistant, and a method for manufacturing the same.

  In order to achieve the above object, the first feature of the present invention is: (a) a semiconductor substrate having a diffraction grating and oscillating by sound pressure; and (b) a light emitting element that irradiates light to the diffraction grating. And a mounting substrate having a light receiving element that detects light diffracted by the diffraction grating and converts it into an electrical signal, and is an optical microphone that converts the displacement of the diaphragm into an electrical signal.

  The second feature of the present invention is that (a) a step of forming a diaphragm having a diffraction grating on a semiconductor substrate, (b) a step of forming a recess for a light emitting element and a recess for a light receiving element on a mounting substrate, and (c) ) Mounting a light emitting element that irradiates light to the diffraction grating in the light emitting element recess, and a light receiving element that detects light diffracted by the diffraction grating and converts it into an electrical signal in the light receiving element recess; The present invention is summarized as a method of manufacturing an optical microphone including a step of causing a concave portion for light and a concave portion for a light receiving element to face a diaphragm and laminating a mounting substrate on a semiconductor substrate.

  According to the present invention, it is possible to provide an optical microphone that has high directivity, is small and thin, and is environmentally resistant, and a method for manufacturing the same.

Before describing the first to fourth embodiments of the present invention, the principle of an optical microphone serving as the basis of these embodiments will be described. First, the basic of an optical microphone is a light diffraction phenomenon by a diffraction grating on a vibrating membrane. Strictly speaking, a two-dimensional diffraction phenomenon must be handled, but a one-dimensional model is used as an approximation for explaining the principle and conceptual design. The intensity distribution of interference fringes by the diffraction grating is expressed by equation (1) (see Toshihiro Arai and Masamitsu Hirai, “Introduction to Optical Engineering”, Kodansha Scientific):
I = I ₀ (sin β / β) ² (sin Nγ / γ) ² (1)
Here, the parameters γ and β are defined as follows using the angle θ formed with the optical axis, the wavelength λ, the speed of light c, the lattice spacing h, the lattice width b, and the number N of lattices:
γ = k ・ h ・ sinθ / 2 (2)
β = k ・ b ・ sinθ / 2 (3)
Here, k = ω / c and ω = 2πc / λ. As is clear from equation (1), a sharp bright line appears in the direction represented by equation (4), where n is an integer:
sinθ = ± nλ / h (4)
If the bright line represented by the equation (4) is detected by the light detection element, a signal corresponding to the displacement of the vibration film can be obtained.

Details will be described in the following first to fourth embodiments of the present invention with reference to the drawings.

  In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings. Also, the following first to fourth embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the component parts. The material, shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the scope of the claims.

(First embodiment)
As shown in FIG. 1B, the optical microphone according to the first embodiment of the present invention includes a semiconductor substrate 11 having a diaphragm 113 that has a diffraction grating and vibrates due to the sound pressure of a sound wave Φ incident from below. And a mounting substrate 15 having a surface emitting semiconductor laser (light emitting element) 21 that emits light to the diffraction grating and a photodiode (light receiving element) 23 that detects light diffracted by the diffraction grating and converts it into an electrical signal. is doing. The semiconductor substrate 11 and the mounting substrate 15 are bonded together via a glass substrate (transparent substrate) 13. As a result, the first substrate has a three-layer structure including the mounting substrate 15, the glass substrate (transparent substrate) 13 below the mounting substrate 15, and the semiconductor substrate 11 disposed below the glass substrate (transparent substrate) 13. The optical microphone which concerns on embodiment is comprised, and the displacement of the diaphragm 113 by a sound pressure is converted into an electrical signal. This three-layer structure may be integrated by, for example, a heat fusion technique or an adhesive.

  FIG. 1A is a plan view showing a pattern on the back surface of the mounting substrate 15. In the light emitting element 21 mounted in the light emitting element recess 155, as shown in FIG. 1A, bonding pads on the light emitting element 21 and wirings 152c and 152d are connected by bonding wires 162c and 162d (note that When the back surface of the light emitting element 21 is one electrode, for example, the wiring 152d is guided to the back surface of the light emitting element 21, and the bonding pad on the light emitting element 21 and the wiring 152c are connected by the bonding wire 162c. .) The bonding pads on the light emitting element 21 are electrically connected to pads (electrode pads) 151c and 151d via wirings 152c and 152d formed on the surface of the mounting substrate 15, respectively.

  Similarly, the bonding pads on the light receiving element 23 mounted in the light receiving element recess 156 are connected to the wirings 152a and 152b and the bonding wires 162a and 162b (note that the back surface of the light receiving element 23 serves as one electrode. For example, the wiring 152b may be led to the back surface of the light receiving element 23 and the bonding pad on the light receiving element 23 may be connected to the wiring 152a with the bonding wire 162a. The bonding pads on the light receiving element 23 are led to pads (electrode pads) 151a and 151b through wirings 152a and 152b formed on the surface of the mounting substrate 15, respectively, as shown in FIG. .

  As can be understood with reference to FIG. 1B, since the portions of the pads 151a to 151d are exposed in the vicinity of both ends of the glass substrate (transparent substrate) 13, the wiring for driving the light emitting element 21 And the signal extraction wiring from the light receiving element 23 can be electrically connected.

As the material of the mounting substrate 15, various organic synthetic resins, ceramics, glass, semiconductors and other inorganic materials can be used. As the organic resin material, phenol resin, polyester resin, epoxy resin, polyimide resin, fluororesin, etc. can be used, and the base material used as a core when making a plate is paper, glass cloth, glass base Materials are used. A common inorganic substrate material is ceramic or semiconductor. In addition, glass is used when a metal substrate or a transparent substrate is required to enhance heat dissipation characteristics. As the material for the ceramic substrate, alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), beryllia (BeO), aluminum nitride (AlN), silicon nitride (SiC), or the like can be used. Furthermore, a metal-based substrate (metal insulating substrate) in which a polyimide resin plate having high heat resistance is laminated on a metal such as iron or copper may be used. Of these materials, it is preferable to use a semiconductor substrate for the mounting substrate 15 because the light emitting element recess 155 and the light receiving element recess 156 can be easily formed by the photolithography technique and the etching technique similar to the manufacturing process of the semiconductor integrated circuit. .

The semiconductor substrate 11 is illustrated as if it is a single layer semiconductor substrate in FIG.
A composite film such as an SOI substrate described later may be used.

As shown in FIG. 2, the semiconductor vibration film (diaphragm) 113 in a matrix, a plurality of holes of a predetermined depth _{(recess) H i-1,1, ·····,} H i, 1 , H _{i, 2} , H _{i, 3} ,..., H _{i + 2,6} are arranged to form a two-dimensional diffraction grating. The semiconductor diaphragm (diaphragm) 113 formed with such a periodic pattern (two-dimensional diffraction grating) is fixed to the bottom cavity side wall 117 provided on the semiconductor substrate 11 by elastic beams 115a and 115b. Yes. As shown by a two-dot chain line in FIG. 1A, when viewed as a plane pattern, the bottom cavity 17 is provided in the shape of a rectangular frame on the semiconductor substrate. As shown in FIG. 1, the diaphragm 113 is arranged in a rectangular diaphragm shape inside the bottom cavity 17. In FIG. 1A, the elastic beams 115a and 115b are also indicated by two-dot chain lines.

As shown in FIG. 1, the beam of the semiconductor laser (light emitting element) 21 passes through the glass substrate (transparent substrate) 13 and is diffracted by the diffraction grating of the semiconductor vibration film (vibration plate) 113, and again, the glass substrate (transparent substrate). 13, and is detected by a photodiode (light receiving element) 23. At this time, as shown in FIG. 3, the incident position of the photodiode (light receiving element) 23 changes by ΔX depending on the displacement ΔY of the semiconductor diaphragm (diaphragm) 113 by the sound wave Φ, so that the output signal is temporally changed. To change. Assuming that a first-order diffraction bright line with strong diffraction intensity is used, n = 1 in equation (4), and sin θ = λ / h. At this time, the displacement ΔY in the Y direction of the semiconductor diaphragm (vibration plate) 113 by the sound wave Φ and the displacement ΔX in the X direction of the incident position of the photodiode (light receiving element) 23 are:
ΔX = ΔYtanθ (5)
It becomes a relationship. A signal that changes with time depending on the displacement ΔX is a sound wave signal.

From the equation (4), the following equation must be approximately satisfied between the distance L between the light emitting element 21 and the diaphragm 113 and the distance M between the light emitting element 21 and the light receiving element 23:
M / L = tanθ (6)
However, strictly speaking, it is necessary to consider the beam shift due to the refraction phenomenon in the glass substrate (transparent substrate) 13.

  For simplicity, assuming that λ / h = 1/2, that is, the wavelength λ of the laser beam is half the grating interval h, sin θ = 0.5. At this time, since tan θ = 1 / √3 to 0.577, M / L to 0.577 is obtained from the equation (6). Therefore, when the distance L between the light emitting element 21 and the diaphragm 113 is 2 mm, the distance M between the light emitting element 21 and the light receiving element 23 may be designed to be 2 × 0.577 = 1.15 mm. In addition, when the distance L between the light emitting element 21 and the diaphragm 113 is 1 mm, the distance M between the light emitting element 21 and the light receiving element 23 may be designed to be 777 μm.

  As described above, if the optical microphone according to the first embodiment of the present invention is designed so as to satisfy the expression (6), all of the mounting substrate 15, the glass substrate (transparent substrate) 13, and the semiconductor substrate 11 are used. A thin film having a thickness of about 60 μm to 600 μm, preferably about 100 μm to 300 μm, can be formed by bonding three layers, which is suitable for downsizing and thinning.

  Furthermore, according to the first embodiment of the present invention, it is possible to observe a minute vibration displacement of the diaphragm as a large difference in reflected light intensity, and realize an optical microphone that is low in cost and has a limited use range. it can. Therefore, it is possible to provide an optical microphone having high directivity, excellent stability, small and thin, environmental resistance, and high manufacturing yield.

  The optical microphone according to the first embodiment of the present invention can be manufactured by the following procedure. Note that the optical microphone manufacturing method described below is an example, and the optical microphone according to the first embodiment can be realized by various other manufacturing methods including this modification. Of course.

  (A) First, a so-called SOI substrate in which a buried insulating film (SOI oxide film) and a single crystal Si layer (SOI layer) are sequentially stacked on a supporting substrate made of single crystal Si is prepared as the semiconductor substrate 11. Next, a photoresist film (hereinafter simply referred to as “photoresist”) is spin-coated on the surface of the SOI layer. Then, the photoresist is patterned by a photolithography technique. Then, using this photoresist as a mask, the SOI layer is etched by the RIE method or the like, and the pattern of the diaphragm 113 is cut out. At this time, the patterns of the elastic beams 115a and 115b are also formed.

(B) Thereafter, a new photoresist is spin-coated on the surface of the SOI layer. That is, the SOI layer is selectively etched by the RIE method or the ECR ion etching method using a photolithography technique, the RIE method, or the like, and the minute hole H _i as shown in FIG. _{-1,1, ·····, H i, 1} , H i, 2, H i, 3, ·····, dig the H _{i + 2,6,} a reflection type two-dimensional diffraction grating Form. Thereafter, the photoresist is removed.

  (C) Thereafter, a new photoresist is spin-coated on the entire surface. A window portion exposing a region between the elastic beam 115a and the elastic beam 115b around the vibration plate 113 is formed in the photoresist by a photolithography technique. Then, using this photoresist as a mask, the SOI oxide film exposed at the window is selectively removed by RIE or the like, and the support substrate is exposed at the bottom of the window.

  (D) An anisotropic etchant of single crystal Si, for example, a chemical solution such as tetramethylammonium hydroxide (TMAH) is introduced through the window, the support substrate is selectively anisotropically etched, and the cavity ( A cavity) is formed below the diaphragm 113. Further, the support substrate is etched from the back surface to form the bottom cavity portion 17, whereby a diaphragm 113 having a diffraction grating as shown in FIGS. 1 and 2 is formed in the bottom cavity portion 17 of the semiconductor substrate 11. The

  (E) On the other hand, a single crystal Si substrate is prepared as the mounting substrate 15. Then, if the single crystal Si substrate as the mounting substrate 15 is anisotropically etched with TMAH or the like using a photoresist or the like as a mask by photolithography technology, the light emitting element recess 155 and the light receiving element recess 156 are mounted. It is formed on the surface of the substrate 15. Thereafter, a metal film of aluminum (Al), aluminum alloy (Al-Si, Al-Cu-Si), copper (Cu), gold (Au) is deposited by CVD, vacuum evaporation, sputtering, etc., and photolithography technology, RIE The metal film is patterned using an etching technique or the like to form patterns such as pads 151a to 151d and wirings 152a to 152d. For patterning the pads 151a to 151d and the wirings 152a to 152d, a lift-off method may be used, or a selective plating method using a mask similar to the lift-off method may be used. Alternatively, patterns such as the pads 151a to 151d and the wirings 152a to 152d may be formed by a screen printing technique or the like.

  (F) Then, the light emitting element 21 that irradiates the light emitting element concave portion 155 of the mounting substrate 15 with light to the diffraction grating, and the light receiving element 23 that detects the light diffracted by the light receiving element concave portion 156 by the diffraction grating and converts it into an electric signal Are implemented respectively. As shown in FIG. 1B, in order to incline the optical axis of the surface emitting semiconductor laser (light emitting element) 21, the bottom of the light emitting element recess 155 is inclined with respect to the main surface of the mounting substrate 15. In this structure, a light-emitting element 21 may be mounted by inserting a spacer with the bottom of the light-emitting element 21 inclined into a light-emitting element recess 155 having a flat bottom formed by anisotropic etching. For example, a structure in which the bottom of the light emitting element 21 is substantially inclined with respect to the main surface of the mounting substrate 15 may be realized by the shape of solder or conductive adhesive when the light emitting element 21 is mounted. Then, the bonding pads on the light emitting element 21 and the wirings 152c and 152d are connected by bonding wires 162c and 162d. Similarly, the bonding pad on the light receiving element 23 and the wirings 152a and 152b are connected by bonding wires 162a and 162b.

  (G) The light emitting element concave portion 155 and the light receiving element concave portion 156 are opposed to the vibration plate 113, and the mounting substrate 15 is made of semiconductor via the transparent substrate (glass substrate) 13 as shown in FIG. If it is laminated on the substrate 11, the optical microphone according to the first embodiment is completed.

(Second Embodiment)
The light emitting element 21 is not limited to a surface emitting semiconductor laser, but may be an edge emitting semiconductor laser. The optical microphone according to the second embodiment of the present invention has a three-layer structure as shown in FIG. 4, and includes an edge-emitting semiconductor laser (light emitting element) 21 and a light receiving element 23 from above, respectively. The semiconductor substrate 11 includes the mounting substrate 15, the glass substrate (transparent substrate) 13, and the vibration plate 113 that are provided in the light-emitting element recess 155 and the light-receiving element recess 156.

  This three-layer structure is integrated by a thermal fusion technique or an adhesive, like the optical microphone according to the first embodiment. Further, the diaphragm 113 is formed with a periodic pattern (diffraction grating) by a semiconductor process technique (etching technique or photolithography technique), as in the optical microphone according to the first embodiment. . The beam of the edge-emitting semiconductor laser (light emitting element) 21 is reflected by a reflecting mirror 159 provided on the wall of the light emitting element recess 155, and is diffracted by the diffraction grating of the diaphragm 113 after passing through the glass substrate (transparent substrate) 13. Then, it passes through the glass substrate (transparent substrate) 13 again and is detected by the light receiving element 23.

  If a single crystal Si substrate is used for the mounting substrate 15, the light emitting element recess 155 and the light receiving element recess 156 are formed by anisotropic etching such as TMAH, and then gold (Au) or the like is formed on the side wall of the light emitting element recess 155. A reflective mirror 159 can be formed by depositing a metal thin film having a high reflectivity by vacuum evaporation or sputtering. However, even by anisotropic etching alone, the side wall of the light emitting element recess 155 becomes a mirror surface, so that the step of depositing a highly reflective metal thin film can be omitted.

  Similar to the optical microphone according to the first embodiment, since the incident position of the light receiving element 23 changes depending on the displacement of the diaphragm 113, the output signal of the light beam changes with time. This signal becomes a sound wave signal corresponding to sound.

  Other points such as the points where the wirings 152a to 152d are formed on the semiconductor substrate 11 and the method of manufacturing the optical microphone are the same as those of the optical microphone according to the first embodiment, and redundant description is omitted.

  According to the second embodiment of the present invention, similarly to the optical microphone according to the first embodiment, it is possible to provide an optical microphone that has high directivity, is small and thin, and has environmental resistance.

(Third embodiment)
As shown in FIG. 5, the optical microphone according to the third embodiment of the present invention includes a mounting substrate 15 having a surface emitting semiconductor laser (light emitting device) 21 and a light receiving device 23 from the top, a transparent tape (transparent substrate). ) 14 and a three-layer structure of the semiconductor substrate 11 having the diaphragm 113. FIG. 5A is a plan view of the back surface of the mounting substrate 15 seen through from the back surface of the transparent tape (transparent substrate) 14, but the plane of the transparent tape (transparent substrate) 14 is larger than the planar dimensions of the mounting substrate 15. Designed with larger dimensions.

  The three-layer structure shown in FIG. 5 is integrated by a heat fusion technique or an adhesive. A periodic pattern (diffraction grating) is formed on the diaphragm 113 by a semiconductor process technique (etching technique or photolithography technique). The beam of the light emitting element 21 passes through the transparent tape (transparent substrate) 14, is diffracted by the diffraction grating of the diaphragm 113, passes through the transparent tape (transparent substrate) 14 again, and is detected by the light receiving element 23. At this time, as shown in FIG. 3, since the incident position of the light receiving element 23 changes depending on the displacement of the diaphragm 113, the output signal of the light beam changes temporally. This signal becomes a sound wave signal corresponding to sound.

  In the optical microphone according to the third embodiment, tape-like mounting wirings 141, 142, 143, and 144 are formed on a transparent tape (transparent substrate) 14, and pads ( Electrode pads) 153a, 153b, 153c, and 153d are electrically connected to each other. In the light emitting element 21 mounted in the light emitting element recess 155, as shown in FIG. 5A, the bonding pads on the light emitting element 21 and the chip-side wirings 154a and 154d are connected by bonding wires 164a and 164d. (If the back surface of the light emitting element 21 is one electrode, for example, the chip side wiring 154a is led to the back surface of the light emitting element 21, and the bonding pad on the light emitting element 21 and the chip side wiring 154d are connected. It may be connected by a bonding wire 164d). The bonding pads on the light emitting element 21 are electrically connected to pads (electrode pads) 153a and 153d through chip-side wirings 154a and 154d formed on the surface of the mounting substrate 15, respectively.

  Similarly, the bonding pads on the light receiving element 23 mounted in the light receiving element recess 156 are connected to the chip-side wirings 154b and 154c by the bonding wires 164b and 164c (note that the back surface of the light receiving element 23 is one electrode). In this case, for example, the chip side wiring 154c may be guided to the back surface of the light receiving element 23, and the bonding pad on the light receiving element 23 and the chip side wiring 154b may be connected by the bonding wire 164b. The bonding pads on the light receiving element 23 are respectively connected to pads (electrode pads) 153b and 153c via chip-side wirings 154b and 154c formed on the surface of the mounting substrate 15, as shown in FIG. Led. These pads 153a to 153d and chip side wirings 154a to 154d can be formed by the chip wiring technique as described in the method of manufacturing the optical microphone according to the first embodiment. In this way, the electrical connection between the drive wiring of the light emitting element 21 and the signal extraction wiring from the light receiving element 23 becomes possible via the mounting wirings 141, 142, 143, 144 on the transparent tape (transparent substrate) 14.

  Other points such as the method of manufacturing the optical microphone are substantially the same as those of the optical microphones according to the first and second embodiments, and thus redundant description is omitted.

  According to the third embodiment of the present invention, similarly to the optical microphones according to the first and second embodiments, it is possible to provide an optical microphone having high directivity, small, thin, and environmentally resistant. Can do.

(Fourth embodiment)
As shown in FIG. 6, in the fourth embodiment of the present invention, a plurality of light-emitting elements 21B and 21A and a plurality of light-receiving elements 23B and 23A are separated from a plurality of diaphragms 113B and 113A having different resonance characteristics. A description will be given of an optical microphone to which a function of selecting a frequency component of sound is obtained by independently obtaining the vibration information.

  FIG. 6 is a plan view showing a pattern on the back surface of the mounting substrate 15. As shown in FIG. 6, the optical microphone according to the fourth embodiment includes a high frequency light emitting element 21B in the light emitting element recess 155B, a low frequency light emitting element 21A in the light emitting element recess 155A, and a light receiving element recess. A high frequency light receiving element 23B is mounted on 156B, and a low frequency light receiving element 23A is mounted on the light receiving element recess 156A. Although illustration of a cross-sectional structure is omitted, it is basically the same as the optical microphone according to the first embodiment, and the mounting substrate 15 on which the light emitting elements 21B and 21A and the light receiving elements 23B and 23A are mounted from above, glass The semiconductor substrate 11 has a three-layer structure including a substrate (transparent substrate) 13, a high-frequency diaphragm 113B, and a low-frequency diaphragm 113A. In FIG. 6, the high-frequency diaphragm 113 </ b> B and the low-frequency diaphragm 113 </ b> A having a larger area than the high-frequency diaphragm 113 </ b> B and the region of the bottom cavity 17 that accommodates these are shown by phantom lines. As long as it is divided into a high-frequency vibration region and a low-frequency vibration region, the high-frequency diaphragm 113B and the low-frequency diaphragm 113A may be an integrated diaphragm.

  As shown in FIG. 6, the high-frequency light-emitting element 21B mounted in the light-emitting element recess 155B has bonding pads on the high-frequency light-emitting element 21B and wirings 152c and 152d connected by bonding wires 162c and 162d (see FIG. 6). When the back surface of the high frequency light emitting element 21B is one electrode, for example, the wiring 152d is guided to the back surface of the high frequency light emitting element 21B, and the bonding pad on the high frequency light emitting element 21B and the wiring 152c are bonded. It may be connected with a wire 162c). The bonding pads on the high-frequency light-emitting element 21B are electrically connected to pads (electrode pads) 151c and 151d via wirings 152c and 152d formed on the surface of the mounting substrate 16, respectively.

  Similarly, the bonding pads on the high frequency light receiving element 23B mounted in the light receiving element recess 156B are connected to the wirings 152a and 152b and the bonding wires 162a and 162b (note that the back surface of the high frequency light receiving element 23B is one side). For example, the wiring 152b may be led to the back surface of the high frequency light receiving element 23B, and the bonding pad on the high frequency light receiving element 23B and the wiring 152a may be connected by the bonding wire 162a. Then, the bonding pads on the high-frequency light receiving element 23B are guided to pads (electrode pads) 151a and 151b via wirings 152a and 152b formed on the surface of the mounting substrate 16, respectively, as shown in FIG.

  On the other hand, in the low frequency light emitting element 21A mounted in the light emitting element recess 155A, as shown in FIG. 6, the bonding pads on the low frequency light emitting element 21A and the wirings 152g and 152h are connected by bonding wires 162g and 162h. (If the back surface of the low-frequency light-emitting element 21A is one electrode, for example, the wiring 152h is led to the back surface of the low-frequency light-emitting element 21A, and bonding is performed on the low-frequency light-emitting element 21A. The pad and the wiring 152g may be connected by the bonding wire 162g). The bonding pads on the low-frequency light emitting element 21A are electrically connected to pads (electrode pads) 151g and 151h via wirings 152g and 152h formed on the surface of the mounting substrate 16, respectively.

  Similarly, the bonding pads on the low frequency light receiving element 23A mounted in the light receiving element recess 156A are connected to the wirings 152e and 152f by bonding wires 162e and 162f (the back surface of the low frequency light receiving element 23A). Is one electrode, for example, the wiring 152f is led to the back surface of the low-frequency light receiving element 23A, and the bonding pad on the low-frequency light receiving element 23A and the wiring 152e are connected by the bonding wire 162e. .) Then, as shown in FIG. 6, the bonding pads on the low-frequency light receiving element 23A are led to pads (electrode pads) 151e and 151f via wirings 152e and 152f formed on the surface of the mounting substrate 16, respectively. .

  The pads 151a to 151h and the wirings 152a to 152h can be formed by the chip wiring technique as described in the method for manufacturing the optical microphone according to the first embodiment. As in FIG. 1 (e), the glass substrate (transparent substrate) 13 has portions 151a to 151h in the vicinity of both ends so that the high-frequency light-emitting element 21B and the low-frequency light-emitting element 21A Electrical connection between the driving wiring and the signal extraction wiring from the high-frequency light-receiving element 23B and the low-frequency light-receiving element 23A becomes possible.

  Other points such as the manufacturing method of the optical microphone are substantially the same as those of the optical microphones according to the first to third embodiments, and thus redundant description is omitted.

  According to the optical microphone according to the fourth embodiment shown in FIG. 6, as shown in FIG. 7, the high frequency vibration spectrum from the high frequency light emitting element 21B, the high frequency light receiving element 23B, and the high frequency diaphragm 113B. B can be obtained, and a low frequency vibration spectrum A from the low frequency light emitting element 21A, the low frequency light receiving element 23A, and the low frequency diaphragm 113A can be obtained. Thus, by obtaining vibration information of different vibration spectra, it is possible to add a function of selecting a frequency component of sound. The frequency component of the sound is selected by obtaining vibration information from a portion having different resonance characteristics on the integrated diaphragm 113 by the plurality of light emitting elements 21B and 21A and the plurality of light receiving elements 23B and 23A. A function may be added.

(Other embodiments)
As described above, the present invention has been described according to the first to fourth embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operational techniques will be apparent to those skilled in the art.

In the optical microphones according to the first to fourth embodiments already described, a photodiode array or CCD as shown in FIG. In FIG. 8, a photodiode array composed of _four photodiodes PD ₁ , PD ₂ , PD ₃ , and PD ₄ is illustrated, but the number of photodiodes is not limited to four, and a one-dimensional array or a two-dimensional array is also possible. But you can. If a photodiode array or CCD is used, sensitivity can be improved by detecting not only the first-order diffracted light but also the second-order diffracted light. Furthermore, the diffracted light from the plurality of diaphragms 113A and 113B described in the fourth embodiment can be detected simultaneously as a time series.

  In the optical microphones according to the first to fourth embodiments, the transparent substrates 13 and 14 have wavelength selectivity so that the wavelength of the light emitting element 21 is transmitted but the background light from the outside is blocked. Noise characteristics may be improved. It is possible to reduce noise from the background light and to increase the sensitivity by reducing the light transmittance of portions other than the region where the light beam passes through the transparent substrates 13 and 14.

  Furthermore, as shown in FIG. 9, microlenses 135A and 135B may be formed on a transparent substrate (glass substrate) 13 to form a microlens array, thereby reducing the diameter of the light beam from the light emitting element 21 and improving the utilization efficiency. . The microlenses 135A and 135B are only required to be formed at a position where the optical path from the light emitting element 21 to the light receiving element 23 through the diffraction grating formed on the diaphragm 113 intersects the transparent substrate (glass substrate) 13. And either 135B or 135B can be omitted. In the first, second, and fourth embodiments, since a normal glass substrate is used as the transparent substrate 13, the diameter of the light beam emitted from the light emitting element 21 is initially small, but the light receiving element (photodiode array) 23. When it reaches the stage, it spreads considerably. Accordingly, a part of the light beam deviates from the sensitive area of the light receiving element (photodiode array) 23, leading to a decrease in sensitivity. On the other hand, as shown in FIG. 9, when the microlenses 135A and 135B are formed on the transparent substrate (glass substrate) 13 by an etching technique or a laser processing technique, the light beam is narrowed and the sensitivity is increased. This is because when the light beam diameter is reduced, even a slight beam position change can be detected by the light receiving element (photodiode array) 23.

Furthermore, in certain cases, it is possible to omit the transparent substrates 13 and 14 in the optical microphones according to the first to fourth embodiments. For example, as shown in FIG. 10A, a second semiconductor substrate 18 in which a surface emitting semiconductor laser (light emitting element) 21 and a photodiode (light receiving element) 23 are integrated is used as a mounting substrate, and a semiconductor vibration film (diaphragm) ) A two-layer structure in which the first semiconductor substrate 11 on which the 113 is formed is bonded by a direct bonding method may be used. In FIG. 10A, a light emitting element 21 and a light receiving element 23 are formed by using an epitaxial growth layer 19 formed on a second semiconductor substrate 18 made of a compound semiconductor, and between the light emitting element 21 and the light receiving element 23. Are electrically isolated by an element isolation region 181 consisting of a high resistance region by irradiation with an insulating film or proton (H ⁺ ). The first semiconductor substrate 11 is preferably silicon (Si) considering the mechanical strength of the thin semiconductor vibration film (vibration plate) 113, but may be a compound semiconductor substrate. However, it is necessary to design the depth from the surface of the first semiconductor substrate 11 to the surface of the semiconductor vibration film (vibration plate) 113 so as to satisfy the expression (6). ) 21 and the distance between the photodiode (light receiving element) 23 can be designed by a photolithography technique, so that miniaturization is easy and the structure is excellent in miniaturization and thinning.

  The light emitting element 21 includes an n-side Bragg reflection film 191, an n-side cladding layer 192, an active layer 193, a p-side cladding layer, a p-side Bragg reflection film 195, a p-side electrode 182 and the like as shown in FIG. What is necessary is just to comprise with the surface emitting semiconductor laser provided. When the surface emitting semiconductor laser shown in FIG. 10B is used as the photodiode as the light receiving element 23, a photodiode having the same forbidden bandwidth as that of the surface emitting semiconductor laser is used. Therefore, it is possible to realize an extremely good optical microphone that is not affected by noise and stray light.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

FIG. 1A is a plan view showing a pattern viewed from the back surface of the mounting substrate which is an element of the optical microphone according to the first embodiment of the present invention, and FIG. It is typical sectional drawing explaining the 3 layer structure which consists of the mounting substrate of the optical microphone which concerns on a form, a glass substrate (transparent substrate), and a semiconductor substrate. It is a typical bird's-eye view for demonstrating the two-dimensional diffraction grating formed in the surface of the semiconductor diaphragm (diaphragm) which is an element of the optical microphone which concerns on the 1st Embodiment of this invention. In the optical microphone which concerns on the 1st Embodiment of this invention, it is a schematic diagram for demonstrating the relationship between the distance of a light emitting element and a diaphragm, and the distance of a light emitting element and a light receiving element. FIG. 4A is a plan view showing a pattern viewed from the back surface of the mounting substrate that is an element of the optical microphone according to the second embodiment of the present invention, and FIG. 4B is a diagram showing the second embodiment. It is typical sectional drawing explaining the 3 layer structure which consists of the mounting substrate of the optical microphone which concerns on a form, a glass substrate (transparent substrate), and a semiconductor substrate. FIG. 5A is a plan view in which the back surface of the mounting substrate is seen through from the back surface of the transparent tape (transparent substrate) that is an element of the optical microphone according to the third embodiment of the present invention. These are typical sectional drawings explaining the 3 layer structure which consists of the mounting substrate of the optical microphone which concerns on 3rd Embodiment, a transparent tape (transparent substrate), and a semiconductor substrate. It is a top view which shows the pattern seen from the back surface of the mounting substrate which is an element of the optical microphone which concerns on the 4th Embodiment of this invention. It is a frequency spectrum for demonstrating the function which selects the frequency component of the sound of the optical microphone which concerns on the 4th Embodiment of this invention. It is typical sectional drawing for demonstrating the photodiode array of the optical microphone which concerns on other embodiment of this invention. It is typical sectional drawing for demonstrating the microlens array of the optical microphone which concerns on other embodiment of this invention. It is typical sectional drawing explaining the 2 layer structure which consists of the 1st and 2nd semiconductor substrate of the optical microphone which concerns on other embodiment of this invention.

Explanation of symbols

11 ... Semiconductor substrate (first semiconductor substrate)
13 ... Transparent substrate (glass substrate)
14 ... Transparent substrate (transparent tape)
DESCRIPTION OF SYMBOLS 15 ... Recessed part 15, 16 ... Mounting substrate 17 ... Bottom cavity part 18 ... 2nd semiconductor substrate 19 ... Epitaxial growth layer 21 ... Light emitting element 21A ... Light emitting element for low frequency 21B ... Light emitting element for high frequency 23 ... Light receiving element 23A ... For low frequency Light receiving element 23B ... High frequency light receiving element 113 ... Vibration plate 113A ... Low frequency vibration plate 113B ... High frequency vibration plate 115a, 115b ... Elastic beam 117 ... Bottom cavity side wall 135A, 135B ... Micro lens array 141, 142, 143 144 ... Mounting wiring 151a-151h, 153a-153d ... Pad 152a-152h ... Wiring 154a-154d ... Chip-side wiring 162a-162h, 164a-164d ... Bonding wire 155, 155A, 155B, 156, 156A, 156B ... Recess 159 ... Reflector 181 ... Elementary Isolation region 182 ... p-side electrode 191 ... n-side Bragg reflection layer 192 ... n-side cladding layer 193 ... the active layer 194 ... p-side cladding layer 195 ... p-side Bragg reflection layer [Phi ... waves _{PD 1, PD 2, PD 3} , PD ₄ … Photodiode

Claims (5)

An optical microphone that vibrates a semiconductor diaphragm having a diffraction grating by the sound pressure of a sound wave incident from the lower surface of the semiconductor diaphragm, and converts the displacement of the semiconductor diaphragm into an electric signal,
A semiconductor substrate having a flat plate-like fixing portion made of a semiconductor, and the semiconductor diaphragm housed in a hollow portion penetrating from the lower surface to the upper surface of the fixing portion and fixed to a side wall of the hollow portion;
A light emitting element recess and a light receiving element recess are provided independently on the surface facing the semiconductor diaphragm, and the light emitting element recess is irradiated with light at an oblique incident angle on the upper surface of the semiconductor diaphragm. A light emitting element is mounted, a light receiving element that detects light diffracted by the diffraction grating of the semiconductor diaphragm and converts it into an electrical signal is mounted in the light receiving element recess, and is laminated on the upper surface side of the fixed part Mounting board,
A transparent substrate that is inserted between the semiconductor substrate and the mounting substrate so that the semiconductor substrate and the mounting substrate are bonded together, and has a lower surface in contact with the upper surface of the fixing portion
A gap portion is provided between the upper surface level of the fixed portion and the upper surface of the semiconductor diaphragm, and a sound wave entrance window is provided between the lower surface level of the fixed portion and the lower surface of the semiconductor diaphragm. A recess is provided,
The light emitting element is surface-emitting type semiconductor light-emitting element, fixed surface of the light emitting element of the recess for the light emitting element, the incident angle equivalent, characterized in that is tilted with respect to the upper surface of the semiconductor diaphragm Optical microphone . An optical microphone that vibrates a semiconductor diaphragm having a diffraction grating by the sound pressure of a sound wave incident from the lower surface of the semiconductor diaphragm, and converts the displacement of the semiconductor diaphragm into an electric signal,
A semiconductor substrate having a flat plate-like fixing portion made of a semiconductor, and the semiconductor diaphragm housed in a hollow portion penetrating from the lower surface to the upper surface of the fixing portion and fixed to a side wall of the hollow portion;
A light emitting element recess and a light receiving element recess are provided independently on the surface facing the semiconductor diaphragm, and the light emitting element recess is irradiated with light at an oblique incident angle on the upper surface of the semiconductor diaphragm. A light emitting element is mounted, a light receiving element that detects light diffracted by the diffraction grating of the semiconductor diaphragm and converts it into an electrical signal is mounted in the light receiving element recess, and is laminated on the upper surface side of the fixed part Mounting board,
A transparent substrate that is inserted between the semiconductor substrate and the mounting substrate so that the semiconductor substrate and the mounting substrate are bonded together, and has a lower surface in contact with the upper surface of the fixing portion
A gap portion is provided between the upper surface level of the fixed portion and the upper surface of the semiconductor diaphragm, and a sound wave entrance window is provided between the lower surface level of the fixed portion and the lower surface of the semiconductor diaphragm. A recess is provided,
The light-emitting element is an edge-emitting semiconductor light-emitting element;
An optical microphone , further comprising a reflecting mirror for causing light from the light emitting element to enter the upper surface of the semiconductor diaphragm from an oblique direction in the recess for the light emitting element. The transparent substrate is transmitted through the wavelength of the light emitting element, an optical microphone according to claim 1 or 2, wherein the background light from the outside having wavelength selectivity for blocking. A method of manufacturing an optical microphone, wherein a semiconductor diaphragm having a diffraction grating is vibrated by sound pressure of a sound wave incident from the lower surface of the semiconductor diaphragm, and the displacement of the semiconductor diaphragm is converted into an electric signal,
A semiconductor substrate is provided with a flat plate-shaped fixing portion made of a semiconductor and the semiconductor diaphragm housed in a hollow portion penetrating from the lower surface to the upper surface of the fixing portion and fixed to a side wall of the hollow portion. Forming the diffraction grating on the diaphragm;
Forming a light emitting element recess and a light receiving element recess on one surface of a flat mounting substrate;
Mounting a light emitting element in the light emitting element recess, and mounting a light receiving element in the light receiving element recess;
The light of the light emitting element is incident on the upper surface of the semiconductor diaphragm at an oblique incident angle, and the light diffracted by the diffraction grating of the semiconductor diaphragm is detected by the light receiving element and converted into an electrical signal. The light emitting element recess and the light receiving element recess are opposed to the vibration plate, and the mounting substrate is bonded to the semiconductor substrate via a transparent substrate having a lower surface in contact with an upper surface of the fixing portion. Laminating on the upper surface side of the fixed portion of the semiconductor substrate
A gap portion is provided between the upper surface level of the fixed portion and the upper surface of the semiconductor diaphragm, and a sound wave entrance window is provided between the lower surface level of the fixed portion and the lower surface of the semiconductor diaphragm. A recess is provided,
The light emitting element is a surface emitting semiconductor light emitting element;
In the step of forming the recess for the light emitting element on the mounting substrate, the fixing surface of the light emitting element of the recess for the light emitting element is formed to be inclined with respect to the upper surface of the semiconductor diaphragm by an amount corresponding to the incident angle. A method of manufacturing an optical microphone. A method of manufacturing an optical microphone, wherein a semiconductor diaphragm having a diffraction grating is vibrated by sound pressure of a sound wave incident from the lower surface of the semiconductor diaphragm, and the displacement of the semiconductor diaphragm is converted into an electric signal,
A semiconductor substrate is provided with a flat plate-shaped fixing portion made of a semiconductor and the semiconductor diaphragm housed in a hollow portion penetrating from the lower surface to the upper surface of the fixing portion and fixed to a side wall of the hollow portion. Forming the diffraction grating on the diaphragm;
Forming a light emitting element recess and a light receiving element recess on one surface of a flat mounting substrate;
Mounting a light emitting element in the light emitting element recess, and mounting a light receiving element in the light receiving element recess;
The light of the light emitting element is incident on the upper surface of the semiconductor diaphragm at an oblique incident angle, and the light diffracted by the diffraction grating of the semiconductor diaphragm is detected by the light receiving element and converted into an electrical signal. The light emitting element recess and the light receiving element recess are opposed to the vibration plate, and the mounting substrate is bonded to the semiconductor substrate via a transparent substrate having a lower surface in contact with an upper surface of the fixing portion. Laminating on the upper surface side of the fixed portion of the semiconductor substrate
A gap portion is provided between the upper surface level of the fixed portion and the upper surface of the semiconductor diaphragm, and a sound wave entrance window is provided between the lower surface level of the fixed portion and the lower surface of the semiconductor diaphragm. A recess is provided,
The light-emitting element is an edge-emitting semiconductor light-emitting element;
After the step of forming the recess for the light emitting element on the mounting substrate, the step of providing a reflecting mirror for causing the light from the light emitting element to enter the upper surface of the semiconductor diaphragm from an oblique direction in the recess for the light emitting element. An optical microphone manufacturing method comprising:

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